Cholera today-With animated answers-

Vibrio cholerae, reported cases,

7th pandemic, incidence trend, prevention,

treatment and vaccines

By Severa von Wentzel & Mary Doherty

September 2014

Vibrio cholerae (1)

• “Cholera is an acute intestinal infection caused by ingestion of food or water contaminated with the bacterium Vibrio cholerae 01 or 0139. It has a short incubation period and produces an enterotoxin that causes copious, painless, watery diarrhoea that can quickly lead to severe dehydration and death if treatment is not promptly given. Vomiting also occurs in many patients.

• About 75% of people infected with V. cholerae 01 or 0139 do not develop any symptoms and become ill, although the bacterium is present in their faeces for 7-14 days.(WHO)

• When illness does occur, about 80-90% of episodes are of mild or moderate severity and are difficult to distinguish clinically from other types of acute diarrhoea. Less than 20% of ill persons develop typical cholera with signs of moderate or severe dehydration.” (Source:

http://www.who.int/topics/cholera/about/en/ )

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Action for students:

Note the following in your records:

• Name of the disease

• Causative agent

• Incubation period

• Mode of transmission

• Degree of infectiousness

• Symptoms

• Treatment

• Mortality statistics

You may find the previous slide and these sources helpful:

• WHO http://www.who.int/topics/cholera/about/en/

• CDC http://www.cdc.gov

• Vibrio cholerae powerpoints

http://www.bing.com/search?q=Vibrio+cholerae+-+Columbia+University&src=IE-SearchBox&Form=IE8SRC

http://www.pitt.edu/~super1/lecture/lec19901/index.htm

• Youtube video on cholera: http://www.youtube.com/watch?v=KPjOMpM8JbE

http://msf.org.uk/schools-resources

Vibrio cholerae (2)

Prokaryotic cells diagram

Action for students: Draw and annotate a diagram of a cell.

Image: https://www.boundless.com/biology/cell-structure/prokaryotic-cells/components-of-prokaryotic-cells/

Prokaryotic cells

Key points

“Prokaryotes lack an organized nucleus and other membrane-bound

organelles.

Prokaryotic DNA is found in a central part of the cell called the nucleoid.

The cell wall of a prokaryote acts as an extra layer of protection, helps

maintain cell shape, and prevents dehydration.

Prokaryotic cell size ranges from 0.1 to 5.0 μm in diameter.

The small size of prokaryotes allows quick entry and diffusion of ions and

molecules to other parts of the cell while also allowing fast removal of waste

products out of the cell.” https://www.boundless.com/biology/cell-structure/prokaryotic-cells/components-of-prokaryotic-

cells/

More info on prokaryotic cells:

• http://www.ivy-rose.co.uk/Biology/Cells/Prokaryotic-Cell-Structure.php

Action for students: What are the key points about prokaryotic cells?

7th pandemic

Source: http://www.bbc.co.uk/news/health-14664450

Further info on the 7th pandemic: • http://www.cbc.ca/news/technology/cholera-s-seven-pandemics-1.758504

From a single global source - the Bay of Benghal – a major cholera

pandemic has spread in at least three waves. The climate, ecology and

large river deltas of the Bay of Benghal could be why it spread from there.

Within some marine ecosystems the cholera bacteria exists naturally.

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Reported cases

Source: http://www.who.int/gho/epidemic_diseases/cholera/cholera_005.jpg

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Incidence trend

Action for students: What is the trend of cholera incidence based on reported cases? When and where is the risk highest? According to the WHO graph, incidence of cholera spiked in 1991 and

2011 – with a notably large increase in the Americas.

Steady rise since 2005 with outbreaks affecting several continents, then a drop in 2012. There are severe epidemics in Haiti and several African countries.(See UCLA “Cholera in Haiti and the modern John Snow” http://www.ph.ucla.edu/epi/snow/cholera_haiti.html)

Natural and man-made disasters such as earthquakes and floods can drive up the risk of cholera. Cholera is a serious risk in the aftermath of emergencies, like the Haiti earthquake of 2010, but can strike anywhere. The situation can be especially problematic in rainy seasons when houses and latrines flood and contaminated water collects in stagnant pools.

Risk can also be high in “camps for internally displaced population or refugees, where minimum requirements of clean water and sanitation are not met.” (http://who.int/features/factfiles/cholera/facts/en/index4.html)

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Photo: Florian Lems

Clean water supply in Uganda helps refugees from the

Democratic Republic of Congo. MSF’s water and sanitation

engineers and logisticians play a vital role in the prevention of

cholera.

Reporting and surveillance

Action for students:

Only a small proportion of the 3–5 million cholera cases in 56 countries and of the 100 000–120 000 deaths attributable to cholera every year of are reported to the WHO. Suggest reasons why the actual number of cholera cases is much higher than reported?

The actual number is much higher than reported, because of under reporting, limitations in surveillance systems and inconsistencies in definitions.

Surveillance for prevention, preparedness and early warning are an essential tool and can help anticipate potential outbreaks. “Surveillance should guide interventions and lead to timely prevention and preparedness activities. When seasonal occurrence can be anticipated, prevention and control must be enhanced and activities such as preparedness plans, training of healthcare staff and pre-positioning of supplies must take place.”(http://who.int/features/factfiles/cholera/facts/en/index5.html)

Environmental causes of

cholera and response

Action for students: Suggest environmental causes of cholera and how they can be addressed.

Outbreaks are usually caused by contaminated water supply, so tend to erupt where food hygiene, sewage treatment and adequate drinking water treatment are either inadequate or non-existent. Unsanitary conditions increase risk of water and food-borne infections such as cholera and typhoid. Once there is an outbreak, it is paramount that appropriate treatment and control measures are put in place.

Cholera “control depends on far more than the prompt medical treatment of cases.”(WHO) The best means of preventing cholera and other diarrheal diseases are improvements in water supply, sanitation, food safety and community awareness of preventive measures. “The interplay of prevention, preparedness and response focusing on water safety and proper sanitation, together with an efficient surveillance system are paramount for mitigating outbreaks and diminishing case fatality rates.” (http://who.int/features/factfiles/cholera/facts/en/index6.html)

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Cholera is treatable

• Cholera is treatable. Administration of oral rehydration salts (ORS) to replace lost

fluids can successfully treat up to 80% of cases and intravenous administration of

fluids and appropriate antibiotics can be used to treat severe cases.(WHO)

• Cholera, if left untreated, can kill quickly following the onset of symptoms, so treating

patients can save lives and also prevent further outbreaks. The mortality rate of

severe cases is between 30-50%.

MSF cholera treatment

centres

http://msf.org.uk/schools-resources

Action for students: Go to the abstract interactive maps of a cholera

treatment centre and find out about disinfections areas; tents for acute

hospitalisation, recovery, and observation; supplies and pharmacy; and

latrines.• http://www.msf.org.uk/cholera

• http://ctc.msf.org/home/

Photo: Nick Owen/MSF

Where are cholera cases

endemic today? Action for students: Where are cholera cases endemic today?

Articles for reference:

• http://www.who.int/gho/epidemic_diseases/cholera/en/

• http://gamapserver.who.int/gho/interactive_charts/cholera/atlas.html

• http://reliefweb.int/report/world/cholera-haiti-africa-and-beyond

Cholera is now very rare in industrialised countries, where measures for

sanitation, prevention, diagnosis and quarantine are in place. It is endemic and

can still cause large numbers of deaths of people living under poor socio-

economic conditions in areas of poor sanitation, crowding and malnutrition.

As was the case in mid-nineteenth century Britain, large-scale migration into

urban centres and accompanying growth of urban tenements and slums in less

developed countries can result in living conditions with risk for the spread

of cholera if the organism exists or is introduced into the environment.

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MSF cleans wells after floods in the Philippines.

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MSF builds latrines for asylum seekers in Brazil.

Oral cholera

vaccines

• Oral cholera vaccines of demonstrated safety and effectiveness have

recently become available for use by individuals and have become part of

the cholera control package. Some countries have already used oral

cholera vaccines to immunize populations considered to be at high risk for

cholera outbreaks.

• Evidence gained on the use of oral cholera vaccines is evolving rapidly.

Work is under way to investigate the role of mass vaccination especially of

vulnerable populations in high-risk areas as a public health strategy for

protecting at risk populations against cholera.

• Issues being addressed include logistics, cost, timing, vaccine production

capacity, and criteria for use of mass vaccination to contain and prevent

outbreaks.” (source http://www.who.int/topics/cholera/vaccines/en/)

• There is no country that requires proof of oral cholera vaccination at

present. (http://who.int/features/factfiles/cholera/facts/en/index8.html)

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Oral vaccination

programmes

© MSF

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“Oral cholera vaccines have opened up the possibility of preventing outbreaks

among the most vulnerable populations living in high risk areas, where

usually recommended control measures are not sufficient.”(http://www.who.int/cholera/vaccines/en/)

Further info on cholera vaccines:

• WHO http://www.who.int/topics/cholera/vaccines/en/

• Research article on cholera vaccination programme:

http://www.plosmedicine.org/article/info%3Adoi%2F10.1371%2Fjournal.pmed.1001512

• MSF press release use of oral cholera vaccine in Guinea

http://www.doctorswithoutborders.org/press/release.cfm?id=7114&cat=press-release

South Sudan:

The food insecurity situation in Upper Nile and consequent

malnutrition leaves the population more susceptible to cholera.

MSF and cholera

• MSF has treated cholera outbreaks in Algeria, Angola,

Cameroon, the Democratic Republic of Congo, Haiti,

India, Kenya, Nigeria, Pakistan, Papua New Guinea,

Somalia, South Sudan, Uganda and Zimbabwe.

• In 2012, MSF admitted 57,400 people to cholera

treatment centres; in 2013, it admitted 27,900.

• In many situations, MSF teams have limited the death

rate to less than one percent.

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Thank you for using our resource. We would be pleased to receive your

feedback. Email: schools@london.msf.org.

Find out more about MSF: http://www.msf.org.uk